Natural killer (NK) cells kill infected and malignant cells and direct subsequent adaptive immunity. NK cells distinguish normal from aberrant cells largely via killer cell immunoglobulin-like receptors (KIR). Despite high homology between KIR genes, individual NK cells express distinct numbers and combinations of clonally-restricted KIR (crKIR) genes. In contrast to crKIR, KIR2DL4 is expressed by all NK cells, preceding crKIR expression during NK development. The long-range goal is to use NK cells as effective treatments of cancer and infectious diseases. As the next logical step toward that goal, the current objectives are to further characterize KIR expression control in normal physiology and during epigenetic therapy of lymphoma and myelodysplastic syndrome. The rationale for the proposed research is that once KIR gene regulation is better understood, then KIR expression can be manipulated to make effective NK cells reagents in immunotherapy of cancer and infectious diseases. In this proposal, 2DL4 and crKIR promoters will be investigated, with special attention to mechanisms that overcome DNA methylation and repressive chromatin. Because so little is known about how lymphocyte-specific gene expression is influenced by cancer and by epigenetic therapy, we will study how DNA methylation and histone deacetylase inhibitor drugs affect KIR promoter methylation, KIR expression, and NK cell activation in myelodysplastic syndrome and lymphoma patients. This work may explain why NK function is poor in cancer patients and might suggest strategies for boosting immunity in these patients. We will catalog NK cell microRNA expression and their target mRNAs and we will investigate the microRNA mechanisms that regulate dangerous cytotoxic NK cells and unlicensed inhibitory receptor- negative NK cells. This will provide the basic information needed for future studies on control of NK developmental decisions in health and disease. This study will 1) develop a clear understanding of the multiple layers of regulation that control the initiation and maintenance of KIR expression; 2) establish for the first time how epigenetic therapy affects nonmalignant human lymphocyte gene expression and function in vivo; and 3) reveal NK-specific microRNA patterns and elucidate how they control mRNA targets to regulate NK development and set NK cell activation thresholds. These results will be highly significant, because they will be essential for understanding how NK cells distinguish normal from aberrant cells. Such an understanding will suggest new ways to manipulate NK cells in the therapy of cancer and infectious diseases. PUBLIC HEALTH RELEVANCE: Natural killer (NK) cells kill infected and malignant cells and direct subsequent adaptive immunity. The long-range goal is to use NK cells as effective treatments of cancer and infectious diseases. As the next logical step toward that goal, the current objectives are to further characterize NK gene expression control in normal physiology and in cancers and pre-cancers, such as lymphoma and myelodysplastic syndrome.